
In Auto Racing, the Blue Flag without the yellow diagonal stripe is used in NASCAR, IndyCar, and FIA-sanctioned championships for different rulings. In NASCAR it is used to mean the course is partially blocked or stopped car on road courses only and is also used for hard to see hazards that are ahead.
In IndyCar, the flag is used to mean that the lapped car must give way to faster cars approaching and also means that the approaching car is attempting to overtake.
In FIA-sanctioned championships, the flag is used to only mean that the lapped car must give way to faster cars approaching. If the driver fails to give way to the faster car three times in a row, then they are subject to a drive-through penalty.
This flag is not used in iRacing, instead its the Blue flag with yellow diagonal stripe (Courtesy Flag).
NASCAR (road course only): Course is partially blocked, stopped car on course, hard to see hazard ahead.
IndyCar: Lapped Car must give way to faster cars approaching, approaching car is attempting to overtake.
FIA-sanctioned championships: Lapped car must give way to faster cars approaching.